Method and apparatus for producing diffracted-light contrast enhancement in microscopes

ABSTRACT

A plate ( 130 ) with a convex edge ( 137 ) which is inserted within the optical path ( 190 ) of a microscope ( 100 ) produces a chromatic region ( 230 ). Refractive specimens ( 240 ) illuminated by this chromatic region ( 230 ) have enhanced contrast and an improved three-dimensional shadowcast effect. The plate ( 130 ) is small enough to only block a minority of light passing through the optical path ( 190 ), and is centrally located within the optical path ( 190 ) to minimize astigmatic error. The plate ( 130 ) may be manufactured simply and durably, and is readily applied to existing microscopes as an add-on tool for viewing specimens. Additional methods are disclosed for making and using the plate ( 130 ) which offer further advantage and benefit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claim priority to U.S. application Serial No.60/098,863, filed Sep. 2, 1998, entitled “Edge-Wave Contrast Enhancementfor Microscopes,” and also to U.S. application Serial No. 60/110,627,entitled “A Device for Producing Diffracted-Light Contrast Enhancementin Microscopes,” filed Dec. 2, 1998, the contents of each which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains most generally to optics systems and elements,and more particularly to illumination systems within bright-fieldmicroscopes. Through the teachings of the present invention, lightcontrol within the optical path of the microscope is achieved byrotating an opaque, convex element through the light path to produce ahighly beneficial contrast enhancement.

2. Description of the Related Art

Microscopes are well-known to provide magnification of small portions orsamples of living or inanimate material. A sample prepared for viewingthrough the microscope is most generally referred to as the specimen,and may be a living biological organism, or may alternatively be othermatter, whether organic or inorganic in origin. Optical bright-fieldmicroscopes, which are the subject of the present invention, magnifyimages formed from light passing through and about a sample for viewingof features that are ordinarily too small to be seen clearly with thenaked eye. The sample may be translucent, transparent, or have somecombination of varying opacity that may include opaque material as well,though with bright-field microscopes as referred to herein, the samplesmust have some translucence through which light may pass for viewing.The sample may also vary greatly in size, though in most instances thespecimen is a relatively small sample of matter such as may be readilyplaced upon a carrier referred to as the slide. For those less familiarwith microscopy, the slide acts as a holder substrate upon which therelatively small specimen may be supported, for transport to themicroscope for viewing and, depending upon the specimen, potentially forsubsequent storage or archiving. In bright-field microscopy, the slidewill most preferably be of an optically transparent or translucentmaterial, and is frequently fabricated from transparent glass.

Within the bright-field microscope, light generated by a light source istypically gathered by a collector lens and concentrated by a condenserupon the stage of the microscope. The specimen is mounted upon thestage, and the light passes through and about the specimen. The image isthen magnified through a combination of objective lens and eyepiece orocular lens, for subsequent viewing or photographing.

Bright-field microscopy is quite old, and is not limited to theinclusion of condensers or collector lenses. Prior art microscopes havebeen used with light-gathering mirrors and other structures that usealternative light sources such as sunlight and other natural light, aswell as artificial lights that have been generated from lanterns andcandles as well as electric light bulbs. As is known to those working inthe field, electric light bulbs offer a particularly convenient andpredictable source of light, and so today most laboratory grademicroscopes include some combination of bulb, collector lens andcondenser.

Various adaptations and techniques have been developed through time toenhance bright-field microscopes. A frequent goal is to improvedetection and differentiation of features within a specimen. Among themore well documented methods are staining of biological specimens,illumination at oblique angles, and various contrast enhancingtechniques such as phase-contrast, differential interference contrast,and single-sideband microscopy. By staining a specimen, differences inpermeability and/or absorption of the stain lead to visual distinctionsbetween various components of the specimen, and can assist greatly inthe identification of the specimen. Unfortunately, once stained, thespecimen is not readily returned to the state it was in prior tostaining. As a result, a single specimen may not be readily analyzed bymultiple methods including staining unless the staining is preserved fora last action. Unfortunately then, all other data desired to be gatheredmust be completely collected prior to staining, other than that derivedfrom the staining, and no second party verification or confirmation ispossible once the staining is complete. If the staining should reveal aneed for further testing, absent the stain, such testing will not bepossible on that sample. Particularly where samples are only availablefor testing in limited supply, or where independent review at differenttimes is preferred, this drawback of staining can be quite undesirable.

Unlike staining, other methods are non-destructive and do not alter thespecimen. Illumination at oblique angles produces visible reflection andrefraction at the interfaces between materials having even relativelysmall differences in indices of refraction. Several techniques have beenproposed for oblique illumination, including the use of an eccentricmount in association with the condenser aperture, variously referred toas the iris diaphragm or condenser diaphragm, and herein referred to asthe aperture diaphragm. By using an eccentric mount, the aperturediaphragm may be shifted from a central position, which passes an equalamount of light from all directions about the central optical axis, toan off-axis position which only passes illumination from one side of thecentral optical axis through the condenser to the stage. This technique,which is discussed for example by H. N. Ott in U.S. Pat. No. 863,805,does result in a shadowcast image with improved contrast. However,resolution of smaller features within the specimen is sacrificed, anddepth of field is undesirably increased due to the reduced numericalaperture of the condenser. For those less familiar with bright-fieldmicroscopes, depth of field represents the distance which is in focusalong the axis of light transmission through the sample. For aninfinitely thin sample, depth of field is not particularly significant.However, as one might imagine, when the sample gets thicker along theaxis of light transmission, which it will in all living samples, therewill be more and more features within the optical path. If many of thesefeatures remain in focus, which is what happens as the depth of fieldincreases, then the image will become progressively more cluttered.Since a more cluttered viewing field makes identification of featuresmore difficult, an increased depth of field is usually quiteundesirable.

A similar technique is also illustrated by Ott in U.S. Pat. No.1,501,800, as well as by Diggins in U.S. Pat. No. 2,195,166, where theyeach illustrate a concave-shaped oblique light diaphragm which ismounted adjacent the iris diaphragm. The oblique diaphragm includes aleaf which partially and progressively blocks light from one side of thediaphragm as the leaf rotates into the light path from one side thereof.Unfortunately, while the oblique light diaphragm is an improvement whichless reduces the numerical aperture of the condenser than the earlierOtt patent, the depth of field is still increased by these Ott andDiggins inventions, and the resultant image is less than desirable.Furthermore, and as will be described in more detail hereinbelow withreference to the present invention, the concave surface illustrated byOtt and Diggins offers undesired interference in the resultant lightpath, which results in less contrast and a more two-dimensional image.

Rehm, in U.S. Pat. No. 3,490,828 illustrates another obliqueillumination method, this time varying the light source from an on-axismirror to a second off-axis mirror, the off-axis mirror which may bepositioned for diverse angles of light incident upon the stage andspecimen. While this invention offers the advantage of not significantlyaltering the depth of field which is in focus, thereby allowing a viewerto focus on relatively narrow vertical sections within a specimenwithout visual clutter, the Rehm invention requires a specially designedmicroscope, and may not be readily retrofit onto existing microscopes.Further, the Rehm invention does not offer advantages which are inherentin the use of diffracted light, this feature which will be discussedmore fully hereinbelow with regard to the present invention. Instead,the Rehm invention is limited to oblique, full wave incident light. Asimilar off-axis mirror system is illustrated by Greenberg in U.S. Pat.Nos. 5,345,333 and 5,592,328, which also suffers from the samedisadvantages and drawbacks.

Other various contrast enhancing techniques modify the illuminatingbeam, generally by altering the condenser by the inclusion of specialapertures, polarizers and prisms, or half-masks. The resulting image isthen filtered or modulated at the image plane of the objective lens.These techniques require several additional components and, frequently,fairly sophisticated image analyzers or electronic contrast enhancement.Examples of these are found, for example, in U.S. Pat. No. 4,407,569 toPiller et al; U.S. Pat. No. 5,394,263 to Galt et al; U.S. Pat. Nos.5,673,144 and 5,715,081 to Chastang et al; U.S. Pat. Nos. 5,684,626 and5,706,128 to Greenberg; U.S. Pat. No. 5,703,714 to Kojima; and U.S. Pat.No. 5,729,385 to Nishida et al. While many of these techniques offerimproved image properties, the complexity and cost associated with thesemethods limit their application to only a few special purpose researchgrade microscopes. The techniques are not readily adapted to existingmicroscopes or lower cost student or general laboratory applications.

SUMMARY OF THE INVENTION

In a first manifestation, the invention is a combined device forenhancing contrast of a refractive specimen. The device includes amicroscope having a stage for locating a specimen within an opticalpath, a source of light, and a means for forming an enlarged virtualimage of the specimen. The microscope is combined with a convex edgeplate within the optical path. The convex edge plate alters lighttravelling through the optical path to produce diffracted light, whichilluminates the specimen. According to further features of the firstmanifestation, the convex edge plate is sufficiently wide thatdiffracted light is passed from only one edge onto the specimen, whilethe plate is also sufficiently narrow so as to only block a minority oflight passing through the optical path.

In a second manifestation, the invention is a method for enhancingcontrast of a refractive specimen comprising the steps of diffractinglight within an optical pathway and defocussing the condenser lens byrelative motion between the diffracting means and the condenser lens toilluminate a portion of the refractive specimen with diffracted light.

In a third manifestation, the invention is a diverging chromatic lightsource formed adjacent a juncture between a dark shadow and a brightfield which interacts with a refractive specimen to form distinctiveoptical illumination maximums and minimums, in combination with anoptical display for displaying the distinctive illumination as a majorpart of the field of view within the display.

OBJECTS OF THE INVENTION

A first object of the present invention is to provide acontrast-enhancing illumination method. A second object is to enhancecontrast without altering a specimen, such that the specimen may readilybe preserved unaltered for future or alternative analysis. A thirdobject of the invention is to provide apparatus which may be placedwithin both new and existing microscopes at various locations within theoptical path, and which is not limited to only one or a few types orbrands of microscopes. A further object of the invention is to provide alow-cost apparatus which is readily purchased by owners of existingmicroscopes and which offers image enhancement comparable to much morecostly systems of the prior art. These and other objects of theinvention are achieved by the preferred embodiment, which is describedhereinbelow and which will be best understood in conjunction with theappended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a photographic microscope in combination with apreferred embodiment apparatus of the invention.

FIG. 2 illustrates a preferred embodiment apparatus of the invention ofFIG. 1 from a top projected plan view.

FIG. 3 illustrates the preferred combination of FIG. 1 from a close-upview illustrating the relative proportion of the preferred embodimentapparatus of the invention relative to the field diaphragm of thephotographic microscope.

FIGS. 4a-4 c illustrate a method step of the invention in associationwith the preferred combination.

FIG. 5 illustrates the diffraction of light adjacent the edge of analternative embodiment apparatus from a projected view.

FIG. 6 illustrates the diffraction of light into the bright field regionfrom the alternative embodiment of FIG. 5, from a top plan view.

FIG. 7 illustrates the diffraction of light into the bright field regionfrom a second alternative embodiment apparatus from a top plan view.

FIG. 8 illustrates the diffraction of light into the bright field regionfrom the preferred embodiment apparatus from a top plan view.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, microscope 100 includes a body 102 extendingvertically at a first end from base 104. Body 102 supports at a secondend a body tube 110, which, along with base 104, is sufficiently rigidlyattached to body 102 to provide support for the remaining components ofmicroscope 100. A stage 106 is supported between body tube 110 and base104 which locates a specimen 150 within the optical pathway alongoptical axis 190. Stage 160 is typically supported from withinappropriate structure within body 102 so as to be vertically adjustablecloser to and further from objective 160 by rotation of objective focusadjustment knob 112. Carried with stage 106 is condenser 142 andaperture diaphragm 140 which are moved relative to stage 106 by rotationof condenser focus adjustment knob 114 to move condenser 142 andaperture diaphragm 140 either closer to or further from stage 106.

The optical components of microscope 100 may be thought of asoriginating at light source 120, which will typically have some type ofelectric filament 122 and may typically be a lamp such as a halogen ortungsten bulb. The particular nature of light source 120 is not criticalto the invention, and other sources of light are known to work forparticular applications, even, in some instances, providing preferableresults. Many of the available sources are mentioned hereinabove in thebackground of the invention though nearly any source of illuminationcould conceivably be used. As is the normal practice, a collector lens124 is preferably provided adjacent light source 120 to gather as muchlight as possible from light source 120, thereby maximizing theefficiency of light source 120 and reducing the amount of power andcooling required for operation of microscope 100. Mirror 126 serves todirect horizontally oriented optical energy from light source 120 alonga vertical axis and through field diaphragm 128. Field diaphragm 128serves primarily to control the total amount of light which isultimately delivered to specimen 150, and, in the preferred embodimentcombination of FIG. 1, field diaphragm 128 will most preferably be leftin a wide-open position to allow maximum illumination. Reducing thefield diaphragm 128 aperture will diminish the three-dimensionalshadowcast effect which predominates in the present invention.

In the most preferred combination, edge plate 130 is located adjacentfield diaphragm 128. Edge plate 130 is located within the generaloptical pathway indicated by optical axis 190, and as a result doesblock some light which would otherwise have passed through fielddiaphragm 128 and into condenser 142. Nevertheless, edge plate 130 willmost preferably only block a minor percentage of the light passingthrough field diaphragm 128. After passing through field diaphragm 128and interacting with edge plate 130, light will next pass throughaperture diaphragm 140 which is adjacent condenser 142. Aperturediaphragm 140 will, in the preferred combination, also be left as openas possible so as to admit the maximum amount of light through condenser142. Restricting aperture diaphragm 140 has the strong effect of“stopping down” condenser 142. At low magnifications, this will diminishthe three-dimensional shadowcast effect. At high magnifications thiswill also undesirably increase the depth of field. Condenser 142 servesto focus light through specimen 150 into objective lens 160, which inturn forms a first virtual image of specimen 150. This image is furthermagnified by eyepiece 170, which might, for exemplary purposes only,include eyepiece field lens 172 and eyepiece eye lens 174. For standardviewing in accord with the preferred embodiment, no additional structureis necessary. However, if the microscope is so equipped, photographs maybe taken of the magnified specimen through the use of a camera or filmholder 180 having a shutter 182 and film plane 184.

As can be seen in FIG. 2, edge plate 130 includes a handle 132 whichallows the manipulation of edge plate 130 by human hand, without adverseinteraction with or contamination of adjacent optical components. Handle132 will most preferably be made much thinner than body 134, to reducethe asymmetric disruption of the illuminating beam and any resultingastigmatism that would otherwise disrupt the image. Body 134 is borderedby inactive edges 135, 136 and 138. These inactive edges must besufficiently spaced from active edge 137 to prevent any opticalinteraction within the active region of light cast by edge 137, as willbe described hereinbelow. Otherwise, it is most preferable to maintainthese edges as closely spaced as possible to minimize asymmetricblockage of light and resultant astigmatism. Active edge 137 is mostpreferably convex in geometry, as shown in FIG. 2. The thickness of edgeplate 130 is not critical to the invention, though edge plate 130 ispreferably formed from a relatively thin and lightweight sheet materialsuch as black anodized aluminum, which is selected for thecharacteristics of low cost, ease of manufacture, durability, andinherent optical absorption. Handle 132 may also be stamped simultaneouswith the balance of edge plate 130, or may alternatively be comprised bya small rod or other handle. Nevertheless, other materials havingdifferent properties and relative thickness may be used satisfactorilyin the performance of the invention. While the most preferred embodimentedge plate 130 uses only a single active edge, it is noted herein thatmore than one edge may be designed to act as an active edge. Forexample, edge 138 may also be designed to be active though it will beunderstood that in order to prevent optical interaction between variousedges, edge 138 will be active in a different region of specimen 150than edge 137.

FIG. 3 illustrates the placement of edge plate 130 from a projectedview, to better illustrate the arrangement and relative sizes ofcomponents. As can be seen therein, edge plate 130 forms a minor portionof the cross-section taken along optical axis 190, thereby admitting amajority of light through to condenser 142. As illustrated, handle 132is not fixedly attached to microscope 100. Nevertheless, it will beunderstood that, when desired, one of ordinary skill will be able tomodify handle 132 and microscope 100 to include various attachmentpoints and mechanism, or other devices such as but not limited tobearing structures, that may be used to position edge plate 130 fixedlyto microscope 100. One benefit of the smaller surface area of edge plate130 which blocks light and the central location of edge plate 130, asshown in FIG. 3, is that astigmatism within the image is reduced. Thisonly further benefits the clarity of the image formed by microscope 100.

FIGS. 4a-4 c illustrate the method of the invention as seen througheyepiece eye lens 174. In the preferred embodiment of FIG. 1, edge plate130 will be at the level of field diaphragm 128. When microscope 100 hascondenser 142 adjusted to its usual Koehler position, shown in FIG. 4a,a dark region 210 is evident, which is the shadow cast by edge 137 ofedge plate 130. In the Koehler position, field diaphragm 128 willusually be in focus, and since edge plate 130 is at the same level, edgeplate 130 will also be in focus and will cast a sharp shadow ontospecimen 150 as represented by dark region 210. As can be seen in FIG.4a, there is very little evidence of specimen 150 visible, though alight outline of cell 240 can be detected near the border betweenbright-field region 220 and dark region 210. However, when condenserfocus adjustment knob 114 is adjusted to move condenser 142 eitherslightly up or down from the Koehler position, dark region 210 andbright-field region 220 become separated by a chromatic region 230. Theinitial adjustment produces only a small chromatic region 230 as shownin FIG. 4b, but nevertheless, an additional cell 241 becomes visible,and greater detail of cell 240 becomes visible, including not onlymembrane but also nucleus. Further defocussing results in a broadenedchromatic region 230, as shown in FIG. 4c. This chromatic region 230 maybe adjusted to completely cover the field of view through eyepiece 170.A much larger number of cells within specimen 150 are now visible, andonce again the features within the first visible cells 240 and 241 arenow much clearer. The chromatic region 230 will typically take on arelatively monochromatic blue color if the condenser is positioned justbelow the Koehler position, and a red color if the condenser ispositioned just above the Koehler position, with edge plate 130 at thelevel of field diaphragm 128. While the invention is not solely limitedto any particular theory, the chromatic light is believed to result fromdiffraction along active edge 137 of edge plate 130. Since the overallintensity of light within chromatic region 230 is reduced relative tothe bright field region 220, it is plausible to increase the intensityof the light output by light source 120, though this may not benecessary in many cases.

Edge plate 130 may be positioned at any point essentially throughout thesub-stage illumination path. However, the most preferred location is asshown in FIG. 1, away from condenser 142. The image of edge plate 130will be just slightly out of focus through condenser 142 with specimen150. A second preferred location for edge plate 130 is between lightsource 120 and collector lens 124. Most preferably, and in either of theforegoing more preferred locations, edge plate 130 is supported by body102 at base 104, and does not move when objective focus adjustment knob112 is rotated, nor when condenser focus adjustment knob 114 is rotated.Several significant benefits are enured by this arrangement. First andforemost, there is no need for special spacings or clearance for edgestop 130. Were edge stop 130 to move together with condenser 142, therewould have to be sufficient clearance to allow the motion of edge plate130. Otherwise edge plate 130 must be positioned much more closely tocondenser 142. And yet when edge plate 130 is located closer tocondenser 142, edge plate 130 begins to adversely affect the opticalcharacteristics of microscope 100, including in particular the depth offield and resolution. In addition, movement of the condenser couldundesirably upset the positioning of edge plate 130, or could requiremore complex attachment between edge plate 130 and the surroundingsupport of microscope 100. Furthermore, not all microscopes have readyaccess at any one or more of the preferred locations. The placement ofthe preferred edge plate 130 of the present invention is veryunrestrictive, allowing the present invention to be benefited from witha very wide variety of microscopes while not interfering withpre-existing components. Other benefits may additionally be gained bythe relative motion between condenser 142 and edge plate 130. So, whileedge plate 130 could be placed anywhere in the substage illuminationpath between light source 120 and stage 106, the most preferred regionis at the level of field diaphragm 128. The otherwise more preferredplacement includes anywhere between field diaphragm 128 and light source120.

While not wishing to be bound by any particular theory in those aspectsof the invention which are otherwise understood and demonstrated to beoperational using the techniques described and illustrated herein, FIG.5 does illustrate broader basic principles of the invention. Thesebroader features will be understood by those skilled in the art, upon areview of the present disclosure, to not be limited to any singlephysical structure or apparatus. Instead, these features of the presentinvention enable those skilled in the art to design a potential myriadof embodiments, which are, nevertheless, within the scope of the presentinvention and claims, and are enabled herein. As shown in FIG. 5, edgeplate 130′ has a straight active edge 137′ that extends beyond fielddiaphragm 128. Light rays 10 are blocked by field diaphragm 128 and edgeplate 130′, while rays 12 pass unobstructed by either edge plate 130′ orfield diaphragm 128. A portion of the optical rays 14 will also bediffracted by edge plate 130′ along active edge 137′, forming adiffraction wave represented by rays 14 a, 14 b and 14 c. Thediffraction waves that result from interaction with an edge, representedby rays 14 a-14 c, are known to have regions of chromaticity. Thesechromatic regions are relatively monochromatic as a result of thediffraction occurring at edge plate 130′. As shown in FIG. 5, ray 14 chas a vertical component 18 and a horizontal component 16. Thediffracted rays 14 which form chromatic region 230 are then observed tointeract with specimen 150 at regions of varying refractive index, suchas at cell membranes and within the nucleus of the cell. The diffractedlight is demonstrated herein to interact with these regions of varyingrefractive index to form new constructive (bright) or destructive (dark)interference patterns, or more simple additive and subtractiveillumination regions. In either case, the net effect is substantiallyenhanced contrast which includes both brightening and darkening ofvarious entities and regions within specimen 150.

Several additional features of the present invention serve to furtherrefine and enhance the imaging of a specimen, and these features areillustrated in FIGS. 6-8. As shown in FIG. 6, alternative embodimentedge plate 130′ having a straight active edge 137′ is shown to have adiffraction pattern in the lateral direction transverse to optic axis190 towards bright field region 220, as illustrated by arrows 16′.Arrows 16′ neither diverge nor converge. As shown in FIG. 7, edge plate130″ has a concave active edge 137″ which has a diffraction pattern inthe lateral direction shown by rays 16″ towards bright field region 220.As is evident, these rays tend to converge. As shown in FIG. 8, edgeplate 130 has active edge 137 which is convex in shape. Rays 16 whichare diffracted from active edge 137 towards bright field region 220 tendto diverge.

The use of convex active edge 137 has been demonstrated to providesubstantially better contrast and more three-dimensional images withinan ordinary biological specimen 150 than obtained with straight activeedge 137′, while straight active edge 137′ provides clearer resolutionthan achieved with concave active edge 137″. The use of convex edge 137therefore provides substantial additional advantage. While not wishingto be bound by any particular theory of operation, this advantage isbelieved to be due to the nature of diverging rays 16. In atheoretically perfect optical system, the relationship between rays 16will hold throughout the optical system. However, since all lenses areimperfect due to aberrations, a certain amount of angular deflectionwill occur between rays emanating from adjacent areas of the edge.Furthermore, all real edges are also imperfect, including edge 137, andwill have optically significant defects therein which can misdirectadjacent rays 16. Finally, specimen 150 may also have imperfections thatwould tend towards generating undesired interference. Rays 16 whichdiverge are less prone to optical interference with adjacent rays, dueto the slight divergence. The slight divergence tends to negate theeffects of optically detectable imperfections present in edge 137 andoptical defects present in the remaining optical components ofmicroscope 100. This benefit is further enhanced by the relativemonochromaticity of chromatic region 230, which limits interferingrefraction from other wavelengths that might otherwise tend to blur oreven completely mask the specimen image of the present invention. Otheredge geometries which offer benefit of diverging rays 16 similar toconvex edge 137 are also contemplated, and will be understood by thoseskilled in the art to be included herein.

While, in most cases, it will be desirable to utilize a convex edge, thepresent invention contemplates and enables application of various edgeplates each having differently configured active edges. For example, andas illustrated in FIGS. 6-8, there may be applications requiring edgeplate 130′ with straight edge 137′ or edge plate 130″ with concave edge137″. Owing to the mechanical simplicity of the invention, various edgeplates may be inserted during one viewing session, which will allowmultiple perspectives to be taken of a single specimen. Because edgeplate 130 is most preferably fabricated from a durable material such asanodized aluminum, other surface treated metals, or even plastics,ceramics, composites or any other suitable material, edge plate 130 willbe resistant to damage or breakage. This can be particularly importantin the applications such as school laboratories, where the tools shouldbe both durable and of low cost.

As demonstrated by the preferred embodiment, the relativelymonochromatic diffracted light which is interacted in an additive andsubtractive or constructive and destructive way provides far bettercontrast enhancement and resolution of specimens than heretoforeavailable with other techniques. As a result of the interaction betweendiffracted light, bright-field light and specimen, and the furthercombination of benefits from convex active edge 137, the presentinvention exceeds contrast enhancement achieved by oblique illumination,and equals or exceeds that achieved by the much more complex andexpensive research techniques such as differential interferencecontrast. Since field of depth is not adversely impacted by therelatively small edge plate 130, the image remains clear anduncluttered, as demonstrated by FIGS. 4a-4 c herein.

INDUSTRIAL APPLICABILITY

Within the region jointly accompanied by diffracted rays 14 c and rays12 from FIG. 5, the specimen has greatest contrast. The simultaneousadditive and subtractive nature of reflection and/or interferencepatterns that are created within chromatic region 230 due to theinteraction between diffracted light 14, bright-field illumination 12and specimen 150 yields astounding contrast. Owing to the simple natureof the apparatus required to generate this enhanced contrast, there aremany applications for which the present invention is suited, only one ofwhich is in the area of biological analysis and observation. Other knownapplications of microscopy which have heretofore been difficult due toinsufficient contrast but which provide specimens having varying opticalproperties will also be served by the present invention. Since theobjects of the invention are, as described in the description of thepreferred embodiment, achieved by the present invention, the presentinvention is applicable industrially not only to new microscopes, butalso to low-cost retrofitting of existing microscopes. This retrofitenables enhancement of contrast sufficient to bring heretofore invisiblefeatures into full view through an ordinary eyepiece in an ordinarymicroscope.

While the foregoing details what is felt to be the preferred embodimentof the invention, no material limitations to the scope of the claimedinvention are intended. Further, features and design alternatives thatwould be obvious to one of ordinary skill in the art are considered tobe incorporated herein. For example, while the preferred embodimentillustrates the use of a compound microscope having an internal lightsource 120, the edge plate of the present invention may be implementedin other light paths that originate from other types of sources, and inother optical arrangements besides the preferred compound microscope, aswill be ascertainable by those skilled in the art upon a review of thepresent disclosure. Structures and configurations that provide theequivalent effects as the present edge plate are contemplated herein.Rather than be limited by the disclosure of a single preferredembodiment, the full scope of the invention is instead set forth anddescribed in the claims hereinbelow.

I claim:
 1. An apparatus for viewing a refractive specimen, comprising:a microscope having a stage for locating a specimen within an opticalpath, a light source illuminating said optical path, and a means forforming an enlarged virtual image of a first part of said specimen; anedge plate within said optical path having a surface area which blocks apart of said illumination, a convex edge diffracting said illuminationadjacent said edge to produce a chromatic diffraction region, and aperimeter edge which extends from said convex edge and encloses saidedge plate surface area; and means for adjusting a location of saidchromatic diffraction region to illuminate said stage adjacent to abright field region while simultaneously directing diffraction alongsaid perimeter edge to a different region of said specimen.
 2. Theapparatus for viewing a refractive specimen of claim 1, wherein saidchromatic diffraction region fully illuminates said first part of saidspecimen.
 3. The apparatus for viewing a refractive specimen of claim 1,further comprising a second diffracting edge within said perimeter edgewhich is a functional substitute for said convex edge.
 4. The apparatusfor viewing a refractive specimen of claim 1, wherein a width of saidedge plate is sufficient to maintain said perimeter edge diffraction insaid different region, whereby interaction between diffraction from saidconvex edge and said perimeter edge is avoided.
 5. The apparatus forviewing a refractive specimen of claim 1, wherein said surface areablocks a minority of said illumination.
 6. The apparatus for viewing arefractive specimen of claim 1, wherein said means for adjusting is anadjustable condenser lens.
 7. The apparatus for viewing a refractivespecimen of claim 6, wherein said edge plate is located remotely fromsaid condenser lens and said adjusting occurs through relative motionbetween said condenser lens and said edge plate.
 8. The apparatus forviewing a refractive specimen of claim 1, wherein said edge platefurther comprises a rugged, non-frangible material.
 9. The apparatus forviewing a refractive specimen of claim 8, wherein said edge plate iscomprised by a surface-treated metal.
 10. The apparatus for viewing arefractive specimen of claim 1, further comprising a phase whereby saidphase contrast objective lens interacts with said chromatic diffractionregion to successfully analyze said specimen without the further needfor a matched condenser annular aperture.
 11. An apparatus fordisplaying a three-dimensional shadowcast image, comprising: a chromaticlight source producing a chromatic light at an optical juncture betweena dark shadow and a bright field and which diverges towards said brightfield; a refractive specimen illuminated by said diverging light betweensaid dark shadow and said bright field to form distinctive opticalillumination maximums and minimums; and an optical display of thedistinctive illumination as a major part of the field of view.
 12. Theapparatus for displaying a dimensional shadowcast image of claim 11,further comprising a mask within a bright field illumination path whichinteracts with broad-spectrum illumination to produce said divergingchromatic light.
 13. The apparatus for displaying a three-dimensionalshadowcast image of claim 12, wherein said mask is encompassed by saidbroad-spectrum illumination, and said dark shadow is cast by said mask.14. The apparatus for displaying a three-dimensional shadowcast image ofclaim 11, further comprising a means for varying the wavelength andextent of said chromatic light illuminating said refractive specimen.15. A method for enhancing optical contrast of a refractive specimen,comprising the steps of: diffracting light at a first location displacedfrom and preceding said refractive specimen within an optical pathway;defocussing a condenser lens by relative motion between said condenserlens and said first location to illuminate a portion of said refractivespecimen with said light diffracted at said first location; andmagnifying said illuminated portion of said refractive specimen.
 16. Themethod for enhancing contrast of a refractive specimen of claim 15,comprising the additional step of varying the convergence or divergenceof said diffracted light from said first location, thereby varying thecontrast and shadowcast effect.
 17. The method for enhancing contrast ofa refractive specimen of claim 15, wherein said diffracting results frominteraction with a convex edge.
 18. The method for enhancing contrast ofa refractive specimen of claim 15, comprising the additional step ofinserting an edge plate into said optical pathway.
 19. The method forenhancing contrast of a refractive specimen of claim 15, comprising theadditional steps of: passing broad-spectrum optical radiation throughsaid optical pathway; adjusting said edge plate to a central locationrelative to said optical pathway, whereby said broad-spectrum opticalradiation passes around and substantially encircles said edge plate,thereby minimizing astigmatism in said magnified illuminated portion ofsaid refractive specimen.
 20. The method for enhancing contrast of arefractive specimen of claim 15, wherein said step of magnifying furthercomprises inserting a phase contrast lens into said optical pathway.